1. Field of the Invention
The present invention relates to a picture reading device that is suited to be employed in an image forming apparatus, such as a laser printer or an ink jet printer, and in particular to discrimination of the type/surface condition of a recording medium (sheet) or the like.
2. Related Background Art
Conventionally, a plurality of print modes have been provided for an image forming apparatus such as a laser beam printer or an ink jet printer, thereby making it possible to obtain an optimum image regardless of which type of printer sheet is used. However, setting from among the print modes is performed by a user himself/herself at the time of printing, so that it is required for the user to have knowledge for discriminating among types of paper and to perform a cumbersome operation of setting the type of a currently used paper by himself/herself. This leads to a problem that it becomes impossible to obtain an optimum image if the paper type is erroneously set.
In recent years, however, there has been devised an image forming apparatus that detects a difference in quantity between regular reflection light and diffused reflection light reflected by the surface of paper, automatically discriminates the type of the sheet based on a result of the detection, and performs image forming control according to a result of the discrimination, thereby making it possible to obtain an optimum image. FIG. 17 is a cross-sectional view of a printer gloss meter according to the invention disclosed in Japanese Patent Application Laid-Open No. 11-216938. A gloss detector 200 includes a block 210 that is attached to a printed board 220 in a usual manner. A light source tube 212 on an axis 213 and a reflection tube 214 on an axis 215 are formed in the block 210. A light source 216 is positioned inside of the light source tube 212, while a photosensor 222 is positioned inside of the reflection tube 214. With this construction, the photosensor 222 mainly reacts to spectral reflection light, thereby discriminating between low gloss paper and high gloss paper.
Also, there has been invented a method with which a picture of the surface of paper is captured by a CCD area sensor and there is obtained a fractal dimension, thereby obtaining the roughness of paper. FIG. 18 is a process flow diagram showing the basic operation of a smoothness detector according to the invention disclosed in Japanese Patent Application Laid-Open No. 11-271037. First, area irradiation of the surface of a recording medium with light is performed in step 2-1 (this step is denoted as “S2-1” in the drawing, the same applies to the succeeding steps). Following this, a shadow image formed by reflection light resulting from the area-irradiation is read as a plane image by image detecting means including image reading means, and information regarding the tone thereof is detected as multivalued image data (step 2-2). That is, when light is irradiated, reflection light is given shadows due to projections and depressions in the recording medium, with each depressed portion becoming dark and each projected portion becoming bright. Then, this shadow image is detected with a CCD that serves as image reading means. The light and shade information that is multivalued data of the detected image is subjected to image processing by information processing means, thereby measuring and calculating the surface roughness of the recording medium (step 2-3). Following this, a parameter value of image forming is determined and controlled by image forming control means according to the measured and calculated surface roughness (step 2-4). That is, in this conventional example, it is possible to estimate the surface roughness of a recording medium by reading light and shade information from the CCD.
When there is used an image pickup sensor such as an area sensor or a line sensor, however, it is required to perform an enormous amount of calculation, which leads to an increase in circuit scale, elongation of a time taken to perform calculation, and an increase in cost. Also, when there is performed complicated calculation, a large volume of memory is required, which leads to a problem that the apparatus size and cost are increased.